Heat-protected thermoplastic component, particularly a vehicle underside component with integrated heat-protection

ABSTRACT

A component for use in thermally stressed areas of vehicles, e.g. in the area of the engine compartment underside, comprises a thermoplastic part i.e. a supporting layer ( 2 ) that is thermally protected by a metallic foil ( 3 ). In order to improve the adherence of the metallic foil ( 3 ), the metallic foil ( 3 ) is provided with a multitude of folding pockets ( 4 ) anchored in the thermoplastic material of the supporting layer ( 2 ). This creates a positive connection between the metallic foil ( 3 ) and the supporting layer ( 2 ).

The present invention concerns a heat-protected thermoplastic componentaccording to the preamble of claim 1, and in particular a vehicleunderside component with integrated heat-protection.

Thermoplastic materials such as polypropylene are sensitive totemperature and have a high surface emission potential, or they have anincreased heat radiation absorption capacity. This increased absorptionof heat radiation results that the matrix of these plastics is intenselyheat under the influence of locally variable heat radiation in localareas, thus inducing undesirable weak spots in these areas. Therefore,when using such materials in areas which are exposed to an increasedheat radiation, metallic foils are applied which reflect the infraredradiation. Thus the matrix temperature of these plastics in suchprotection areas can be effectively lowered, i.e. the undesired materialmutations such as embrittlement, brittleness etc. can be avoided. Thismeasure allows the use of thermoplastic materials also in environmentswhich are exposed to high temperatures. Without such metallic protectivefoils, components made of thermoplastic material undergo a rapid agingprocess and are not usable in environments with increased infraredradiation.

In particular, thermoplastic components are increasingly utilized inmodern automotive technology, as they are much lighter in comparison tometallic components, can be user-defined and inexpensively formed, andare easy to recycle. This leads to an ever increasing significance ofheat-protection for components used in automotive technology. However,heat protection measures for components in automotive technology haveproven to be extremely difficult to implement because of the extrememechanical strains placed on them such as vibration, wind forces, localtemperature fluctuations etc. Currently, such components are provided ina known manner with a metallic foil at their thermally exposed areas inorder to protect them at these points from increased infrared radiation.Unfortunately, this well-known measure leads to products which only havea short-term life.

Thus, for example, U.S. Pat. No. 5,464,952 describes an acousticallyeffective underfloor component for vehicles, having a core layer made ofa heat resistant and heat insulating fibrous material. This core layerpreferably comprises a non-woven material made of glass fibers, ceramicfibers, basalt wool or mixtures thereof and is provided on both sideswith heat reflecting foils made of aluminium or sheet metal in order toreflect any possible infrared radiation which may impinge. The non-wovenof this underfloor component is provided at least at its peripheralregions with a duroplastic bonding agent in order to attach the metallicfoils to the fibrous non-woven. At the same time this attachmentstiffens the peripheral region, which provides the entire underfloorcomponent with a certain form stability. The heat reflecting foilspreferably comprise a triple laminate foil having a glass fiber layer,an aluminium layer and a thermoplastic polyolefine layer, so that theymay be loosely joined over their entire surface in a form press to thenon-woven which, as a rule, is provided with a duroplastic bondingagent. This component also has a relatively stiff peripheral region anda soft, i.e. pliable central region.

In DE 197 05 511 A1 there is described a component utilized as a heatshield comprising a carrier layer made of a thermoplastic syntheticmaterial and a heat protective layer made of aluminium. Between thealuminium layer and the carrier layer there is provided a thermoplasticconnection layer (a hotmelt adhesive) made of polypropylene (PP),polyester (PET), polyamide (PA) or thermoplastic polyurethane (TPU),which melts during the forming process and to which the aluminium layeris fixedly bonded at the carrier layer. This aluminium layer isdimensioned to be much larger than the area of maximum heat exposure(hot-spot region) and is intended to dissipate the heat which impingeslocally, i.e. essentially convection heat. In order to improve the heatconduction capacity, the aluminium layer utilized preferably has athickness of 0.08 to 0.2 mm and the surface of the heat shield can beprovided with particular deformations. In a preferred embodiment, thisheat shield comprises groove-like depressions which run orthogonally toeach other, and which are designed to improve the stability and thecooling properties of the heat shield. In order to effect this heatconducting function, this metallic heat protection layer can be in theform of an expanded metal.

Unfortunately it has been shown that these known foils which are coveredby a metallic foil and which are subjected to high thermic stress areprone to rapid aging processes, i.e. they remain intact for a shortperiod only. In particular, delamination occurs after a short while insuch underfloor components, which makes the use of such components inthe automobile industry unsuitable. In particular, the hotmelt adhesivebetween the metallic protective foil and the carrier material loses itsadhesive properties due to the accelerated aging process caused by thehigh and constantly changing temperature stress. Furthermore, theparticularly pronounced vibrations in this area of use provoke suchcomponents to rapidly show signs of fatigue, breakage or localdecomposition and can lead to undesirable generation of noise.

From WO 99/44851 it is known to provide a fuel tank with an integratedheat protection, and thereby to perforate the reflective metallic foilsin such a manner, that the perforation protrusions thus produced arebackflowed by thermoplastic synthetic material during the manufacturingprocess, which leads to a positive mechanically locking (clawing orbracketing) engagement and thus to more durable products. Unfortunately,also with these components, the plastics used in the perforation regionsare only inadequately protected against infrared radiation and thus canage more rapidly in these areas.

It is therefore the aim of the present invention to provide aheat-protected thermoplastic component which does not have the mentioneddisadvantages and which retains its adhesive properties over its entiresurface, even after prolonged use under thermic radiation exposure. Inparticular, it is the aim of the present invention to provide aheat-protected and vibration-resistant vehicle underside component witha long life span.

This aim is solved according to the invention by a component having thefeatures of claim 1, and in particular by a component having a carrierlayer made of a thermoplastic synthetic, in particular an LFT (endlessfiber reinforced thermoplast) or a GMT (glass fiber reinforcedthermoplast), and a metallic foil connected at least in part thereto,which comprises a multitude of small folding pockets. These foldingpockets are embedded in the synthetic mass, i.e. they are mechanicallyanchored in the synthetic mass and generate a long-term (i.e. more than1000 hours operating time at a temperature of about 140° C.) constantpeeling resistance W_(s) of, for example, at least 0.15 N/mm²(W_(s)>0.15 N/mm²). This anchorage or bracketing of the metallic foilcan be easily produced during the forming process of said thermoplasticcomponents, in that a knobbed or similarly formed foil is inserted intoa form nest or mold together with the synthetic material to be formed.When the form press is closed, the individual knobs, folds or similarpocket-like elevations are partially compressed, turned-over or foldedand form more or less closed folding pockets. When the component isformed, the thermoplastic synthetic can flow around the individualfolding pockets, and in this way produces a form-fitting or positiveconnection with the metallic foil. The technology to form suchcomponents by means of a forming process does not require any specifictechnical knowledge by the expert and is not the subject of the presentinvention. According to their specific use and function requirements,the individual folding pockets can be variously dimensioned, can beregularly or irregularly arranged, can be coated with other materials,and can be totally or partially circumflowed by plastic. In a preferredembodiment, at least 1 to 5 such folding pockets are arrayed in a sectorof 10 to 30 mm. The foil used is preferably made of aluminium and has athickness of 0.01 to 0.1 mm, but can have a thickness of up to 0.5 mm.

In a further development of the present invention, a heat resistantadhesive is provided between the foil and the synthetic carrier, whichdoes not lose its adhesive properties even under increased thermicstress. It is self-evident that the expert may provide furtherfunctional layers between the aluminium foil and the thermoplast.

The component according to the invention is particularly suitable foruse in regions of motor vehicles which are subjected to thermal stress,for example in the regions of the underside of the engine compartment,the spare wheel compartment, the vehicle tunnel, the dashboard cowl, theexhaust pipe or catalytic converter, etc.

The advantages of the present invention are immediately obvious to theexpert and particularly are to be seen in that, with these components, aclosed foil completely protects the synthetic from infrared radiation,thus preventing any delamination. The peeling resistance, a gage for theadhesive properties and vibration resistance, remains unchanged evenafter prolonged use, i.e. at higher temperatures, and thus can also beused at regions in vehicles which are subjected to particular exposureto heat. Furthermore, the present invention makes a low-cost productionof the inventive components possible, in particular because the shapingprocess of the thermoplastic material and the fixing or attachingprocess of the metallic foil to this material can be accomplished in onesingle method step. Furthermore, it is not necessary to make anyperforations, thus enabling a shorter manufacturing time. Therefore, thecomponents according to the invention do not show any long-term signs offlaking or detachment, even under increased vibration or heat stress andthus, when used in vehicles, do not lead to an undesirable generation ofnoise.

In the following, the invention shall be more closely described with theaid of an exemplary embodiment and with the aid of the Figures. Theseshow:

FIG. 1 a spacial view of a schematically illustrated component accordingto the invention;

FIG. 2 an enlarged section through a schematically illustrated componentaccording to FIG. 1;

FIG. 3 a graphic illustration showing the long-term performance of thepeeling resisitance.

The component 1 shown in FIG. 1 comprises a trough-shaped carrier layer2 which is suitably formed according to its use. In the view shown, ametallic foil 3 is inserted into this carrier layer 2. According to theinvention, this foil 3 comprises a plurality of pocket folds 4 whichmechanically couple the metallic foil 3 to the carrier layer 2. Thecarrier layer is preferably made of a glass fiber reinforced thermoplast(GMB) or a thermoplast filled with endless fibers (LFT). Suitablematerials are well known to the expert. Products having endless fibersusually comprise endless fibers in loops or slings, but can also simplybe filled with long fibers. The metallic foil is preferably made ofaluminium and has a thickness of 0.01 to 0.1 mm. However, it isunderstood that this foil can be made of a different metallic material,and in particular of a thin steel sheetmetal and have a thickness of upto 0.5 mm. Alternatively, a heat resistant adhesive layer (hotmeltadhesive) can be provided between this metallic foil 3 and the carrierlayer 2, or additional heat insulating or acoustically effectivematerials can be inserted. In a preferred embodiment, the metallic foil3 has 1 to 5 inventive folding pockets 4 spaced every 10 to 30 mm. Thesefolding pockets 4 can be differently dimensioned or arranged, accordingto their use requirements.

FIG. 2 shows a schematic view of a section through a component 1designed according to the invention. This has at least on one side ametallic foil 3, which, in the finished component 1, should act as aheat reflecting foil. Aluminium is preferably used for this foil 3. Thisfoil 3 is attached to a carrier layer 2 and comprises folding pockets 4which are embedded in the carrier layer 2. These folding pockets 4result from the forming process and are completely surrounded by thematerial of the carrier layer 2. The shaping of these folding pockets 4leads to a tight coupling, i.e. a form-fitting or positive connection,between the metallic foil 3 and the carrier layer 2. These foldingpockets are easily made by using knobbed or otherwise shaped foils forthe forming process. According to the intended use, these foldingpockets 4 can be differently dimensioned and/or arrayed by the expert.For the present invention it has proven to be particularly beneficialthat, for this type of anchorage, the foil 3 does not have to beprovided with perforations in order to be able to achieve a positiveconnection. In particular, the anchorage regions 6, i.e. the regionshaving the folding pockets 4, are protected against the infraredradiation which damages the thermoplastic material of the carrier layer2. For other purposes, e.g. acoustic purposes, the expert can, ofcourse, provide the foil 3 with perforations and to use a differentmaterial for the carrier layer 2, or to provide a further intermediatelayer between the metallic foil 3 and the carrier layer 2. It is thus atthe discretion of the expert to include an intermediate layer, forexample a hotmelt adhesive, a ceramic layer and/or an acousticallyeffective layer.

During the shaping process, a metallic foil 3, which has previously beenknobbed or has otherwise been provided with geometric deformations, isarranged in a heated form press and is covered with an LFT, GMT or othersuitable synthetic material. Thereby the side having the deformations,especially the knobs, faces the synthetic material and thesedeformations are compressed, crushed or randomly folded when thesynthetic material is applied. This leads to the formation of the pocketfolds according to the invention, which permit the flowable plasticsmaterial to flow behind the individual pocket folds 4 so as tocompletely engulf them. It is thus possible to achieve a positiveconnection in a simple manner. The fibrous plastics material is hardenedduring the shaping process so as to form the desired carrier layer 2. Atthe same time, the curing of the plastics layer 2 results in a secureand long-term stable mechanical connection with the metallic foil 3.

FIG. 3 is a graphical illustration of the measurement results to thepeeling resistance W_(s) with different arrangements A, B, C. Here,W_(s) is understood to mean the ability of the metallic foil to bond tothe thermoplastic carrier part, i.e. a gage for the required energy persurface unit to separate the metallic foil 3 from the carrier layer 2.The values in area (I) pertain to arrangements which have not beensubjected to an aging process, whilst the values in area (II) pertain toarrangements which have been subjected to temperatures of 140° C. duringa period of 1000 hours. The values A(I) and A(II) relate to anarrangement A, for which a conventional metallic hotmelt adhesive(MSK25) was used between an LFT-component and an aluminium foil. Themeasurement results show that no measurable adhesion was obtained.

The values B(I) and B(II) relate to an arrangement B, for which anadhesive being optimized for the bonding of aluminium and polypropylene(HSK15) was used between an LFT-component and an aluminium foil. Themeasurement values B(I) obtained thereby make it clear that with thisarrangement in a non-aged condition, an extremely high peelingresistance W_(s)=1.2 N/mm² can be achieved. However, the measurementvalues B(II) show that the peeling resistance after the aging processW_(s)=0.15 N/mm² is reduced (about 85% reduction of the adhesive value).

The values C(I) and C(II) relate to an arrangement C according to theinvention, in which an aluminium foil provided with form pockets isapplied to an LFT-component, and between this LFT-component and thealuminium foil no adhesive was used. The peeling resistance resultingfrom the inventive arrangement C and without the use of an additionaladhesive, in a non-aged condition, results in a value of W_(s)=0.2N/mm², whilst the peeling resistance for this arrangement C, and after1000 hours heat treatment, has only decreased to W_(s)=0.16 N/mm² (about20% reduction of the adhesive capacity). These measurement results makeevident the efficiency of the present invention. In particular, andwithout a further inventive step, the expert may suitably adjust andoptimize the dimensions and shape of the folding pockets.

1. Heat-protected thermoplastic component (1) having a carrier layer (2)made of a thermoplastic synthetic and an at least partially connectedmetallic foil (3), wherein said foil (3) comprises a plurality offolding pockets (4), which are embedded in the carrier layer (2) andform a positive connection with the carrier layer (2).
 2. Componentaccording to claim 1, wherein the thermoplastic synthetic is an endlessfiber reinforced thermoplast (LFT).
 3. Component according to claim 1,wherein the thermoplastic synthetic is a glass fiber reinforcedsynthetic (GMT).
 4. Component according to claim 1, wherein the metallicfoil (3) is an aluminium foil.
 5. Component according to claim 4,wherein the aluminium foil has a thickness of 0.01 to 0.1 mm. 6.Component according to claim 1, wherein in a sector of 10 to 30 mm thereare arrayed at least 1 to 5 folding pockets.
 7. Component according toclaim 1, wherein, between the metallic foil (3) and the thermoplasticcarrier layer (2) there is provided a hotmelt adhesive.
 8. Componentaccording to claim 1, wherein the peeling resistance W_(s), after aconstant exposure over more than 1000 hours to temperatures of about140° C., has a value of at least 0.15 N/mm².
 9. Component according toclaim 1, wherein the peeling resistance W_(s), after a constant exposureover more than 1000 hours to temperatures of about 140° C., is reducedby no more than 20%.
 10. Component according to claim 1, wherein saidcomponent is a vehicle underside component.